Source: McGraw Hill GMAT

In theory, the Habbendorf rotary engine could be a great racing engine, but in practice, it is not. The reason is that the available fuels do not have sufficient octane to obtain maximum performance from the engine.

The answer to which of the following questions would be most relevant to evaluating the adequacy of the explanation given above for why the Habbendorf rotary engine is not a great racing engine?

A. If the Habbendorf rotary engine were to operate at maximum performance levels, how would its performance compare to that of an engine recognized as a great racing engine?
B. At what level of octane in its fuel does the Habbendorf rotary engine achieve maximum performance?
C. What levels of speed, acceleration, and efficiency must an engine display in order to be considered a “great racing engine”?
D. Could a Habbendorf rotary engine be modified so that it is able to achieve maximum performance with the fuels currently available?
E. If a car equipped with a Habbendorf rotary engine were to race against a comparable car equipped with a great racing engine, by how much would the performance of the great racing engine surpass that of the Habbendorf rotary engine?
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Hi, can someone please post an explanation for this question?.... I am stuck.

Hi everyone..

Went for D...but on careful observation of A...it can be understood why A is correct.

A actually goes an extra step .
The basic is to compare the theoritical performance with actual...Then comes the reason
Option A notes that Habbendorf rotary engine at "maximum performance levels" if compared to "a great racing engine"(in which all the criteria required to consider a racing engine to be "great" has been taken care of) can clearly indicate how good Habbendorf rotary engine is.

gmatexam439 This is what i understand from the question.

The argument runs on two grounds, viz one on the theoretical and other on the practical side.It is already mentioned in the argument that the engine is practically not so great since it has got issue with the octane number of the fuel.So there nothing much to be discussed about the practical aspects {because we already know why practically it is not a great engine} and now we are left with only one question .........."whether theoretically it is a great engine or not?". For that we need to assume our engine working under the ideal condition, that is the engine working on the fuel with ideal octane number and then compare the engine's performance with other great engine.

The fuels do not get maximum performance from the engine, thus the engine is not great.


Using POE:

E. Incorrect. It really has nothing to do with the reasoning and knowing how much it might lose by also gives no help. Two engines could be great, but one still has to perform better.

D. Incorrect. How to make the engine better does not matter in how it performs now.

C. Incorrect. Again this really does not address the issue. It might give us a baseline for some (not necessarily all) performance indicators, but the argument here is that the fuel does not get max performance. We also have no idea what performance the engine currently gets.

B. Incorrect. This lets us know what fuel is needed but doesn't tackle the question of what is the problem with the fuel now.

A. Correct.